1. Field of the Invention
The present invention relates to stable liquid personal skin and hair cleansing compositions based on fatty acid technology.
2. The Related Art
Soap has been a mainstay active for cleansers. Most toilet bars contain this surfactant. That is why they are called soap bars.
Beginning many decades ago synthetic detergents, known shorthand as syndets, have been replacing soap. Among the reasons are that many syndets are milder, foam better and are more stable in liquid formats. Partially a result of a relatively higher melting point, soap is ideal for semi-solids such as bars. Contrary in aqueous liquid formulas, there are structuring and stability problems.
In recent years sustainability of resources has become an issue. Syndets are often petroleum derivatives. Those syndets that are prepared from renewable resources need further reactive chemical processing such as sulfonation and/or alkoxylation. By contrast, soaps are generally obtained from renewable resources. They are neutralized fatty acid salts which through mild chemical processing are readily available from vegetable triglycerides. Relevant technology is found in the disclosures which follow.
GB 2 351 979 B (Arai et al) describes liquid cleansing compositions containing mixtures of alkali metal soaps, anionic surfactants and amphoteric/zwitterionic surfactants. The soap/synthetic surfactant liquid compositions were recognized to have problems with low temperature storage stability. They tend to freeze and thereby cannot be readily pumped from their containers. Isoprene glycol with dipropylene glycol were utilized to solve the problem.
WO 97/27279 (Hamada et al.) discloses a body soap incorporating polyoxyethylene alkyl ether sulfate to reduce stiff skinfeel attributed to the soap. A specific ratio of soap to alkyl ether sulfate is needed to overcome the problem.
WO 96/36313 (Chatfield et al.) relates to aqueous liquid cleansing compositions containing soaps. In this patent, short chain fatty acid (C10 or less) is united with a long chain (C14-C22) fatty acid soap to obtain a skin mild liquid with good lather.
U.S. Pat. No. 4,975,218 (Rosser et al.) reports a single liquid phase clear aqueous soap composition containing ethoxylated nonionic surfactants to enhance mildness. Included in the composition are 10-50% of C12-C18 fatty acid soaps and 5-30% of C8-C22 fatty alcohol having 20 to 50 ethoxylate groups. Preferred mixtures of lauric acid to myristic acid are in a ratio of 1:1 to 1:4.
U.S. Pat. No. 4,486,328 (Knott et al.) describes a clear liquid shampoo containing a mixture of water-soluble C8-C18 fatty acid soap and a zwitterionic detergent. The latter is present in a major proportion, i.e. more than 60% of total fatty acid and zwitterionic detergent, to provide the shampoo with stability and clarity. The mole ratio of zwitterionic detergent (e.g. cocoamidopropyldimethyl betaine) to fatty acid ranges from 1.2:1 to 2.3:1. Liquid compositions containing low levels of zwitterionic detergent are cloudy and show phase separation during storage.
U.S. Pat. No. 5,147,574 (MacGilp et al.) discloses a stable dispersoidal liquid soap personal cleanser. The mixture contains 5-20% saturated higher fatty acid potassium soap and 3-18% of free fatty acids. The weight ratio of soap to free fatty acid is 1:0.5 to 1:1 equivalent to about 62.7% to 45.8% of neutralization of total fatty acids. Preferred fatty acids of the invention are those being fully saturated with low levels of lauric acid and high levels of palmitic and stearic acids.
U.S. Patent Application Publication No. 2005/0020461 A1 (Seki) concerns a cleansing composition containing 20-50% of fatty acids and fatty acid salt (soap) mixtures in which 50-80% have 16 or higher carbon atoms. The higher chain lengths are used to improve both mildness and storage stability. High levels of lauric and myristic acids are not preferred due to the after-cleansing tight skinfeel and poor storage stability.
U.S. Pat. No. 6,812,192 B2 (Ribery) reports a foaming liquid for cleansing or make-up removal. Compositions therein contain fatty acids with degree of neutralization between 50 and 100 weight %. The comparative examples show that liquid cleansers containing partially neutralized fatty acids are unstable. At least one non-betaine amphoteric surfactant and at least one sulphosuccinate-type anionic surfactant are required to achieve stability.
Although there is substantial technology reported in the liquid soap area, none of the references have truly achieved a skin mild system that has highly controlled phase and viscosity stability without necessity to depend on syndets.